JP2018050234A - Imaging apparatus and method of processing imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of reducing the degradation of image quality based on a difference in inclination between a plurality of lamp signals.SOLUTION: The imaging apparatus includes: an OB pixel region which includes an OB pixel whose photoelectric conversion part is light-shielded; an effective pixel region which includes an effective pixel whose photoelectric conversion part is not light-shielded; an analog-digital conversion part which analog/digital converts the signal of the OB pixel by using a first lamp signal, analog/digital converts the signal of the OB pixel by using a second lamp signal, and analog/digital converts the signal of the effective pixel by using the first lamp signal or the second lamp signal; and an arithmetic part which outputs a difference between a reference level based on the digital signal of the OB pixel converted to digital from analog by using the first lamp signal and the digital signal of the effective pixel and outputs a difference between the reference level based on the digital signal of the OB pixel converted to digital from analog by using the second lamp signal and the digital signal of the effective pixel.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an imaging apparatus and a processing method of the imaging apparatus.

  Patent Document 1 discloses an imaging device that performs analog-digital conversion. The imaging device compares the pixel signal based on the photoelectrically converted charge and the reference signal whose level changes with a constant inclination, and outputs based on the time when the magnitude relationship between the pixel signal and the reference signal reaches a predetermined relationship Analog-digital conversion for digitizing the signal is performed to generate imaging data. The reading unit performs first analog-digital conversion using a reference signal having a first inclination and second analog-digital conversion using a reference signal having a second inclination as analog-digital conversion of an imaging signal of a pixel. In addition, the reading unit performs third analog-to-digital conversion using the reference signal having the first inclination and fourth analog-to-digital conversion using the reference signal having the second inclination as analog-to-digital conversion of the zero signal. Then, the imaging apparatus can select either digital data obtained by subtracting the third analog-digital conversion result from the first analog-digital conversion result, or digital data obtained by subtracting the fourth analog-digital conversion result from the second analog-digital conversion result. Is selected for each pixel. The imaging device generates imaging data based on the selected digital data. As a result, high-speed and high-resolution analog-digital conversion becomes possible, imaging data in which vertical lines due to variations in pixel data are canceled can be obtained, an increase in horizontal transfer amount can be reduced, and a decrease in frame rate can be suppressed. be able to.

JP 2011-2111535 A

  However, in Patent Document 1, since the zero signal is a signal of a dummy pixel outside the effective pixel region, a level shift due to a temperature rise during energization is not reflected, and a difference in inclination of the reference signal is not absorbed. Therefore, there is a problem that image quality is deteriorated due to black level offset at the time of analog-digital conversion, or noise such as a vertical line remains and image quality is deteriorated.

  An object of the present invention is to provide an imaging apparatus and a processing method of the imaging apparatus that can reduce image quality deterioration due to a difference in reference level based on a difference in inclination of a plurality of ramp signals.

  The imaging device of the present invention includes an optical black pixel region including a plurality of optical black pixels whose photoelectric conversion unit is shielded from light, an effective pixel region including a plurality of effective pixels whose photoelectric conversion unit is not shielded from light, Using the ramp signal, the optical black pixel signal in the optical black pixel region is converted from analog to digital, and the second ramp signal having a slope larger than that of the first ramp signal is used to convert the optical black pixel signal in the optical black pixel region. An analog-to-digital converter that converts an optical black pixel signal from analog to digital and converts the effective pixel signal from analog to digital using the first ramp signal or the second ramp signal; A conversion unit uses the first ramp signal to analyze the effective pixel signal. When converting from digital to digital, the difference between the reference level based on the digital signal of the optical black pixel converted from analog to digital using the first ramp signal and the digital signal of the effective pixel is output, When the analog-digital conversion unit converts the signal of the effective pixel from analog to digital using the second ramp signal, the optical black converted from analog to digital using the second ramp signal A calculation unit that outputs a difference between a reference level based on the digital signal of the pixel and the digital signal of the effective pixel;

  According to the present invention, it is possible to reduce deterioration in image quality due to a difference in reference level based on a difference in inclination of a plurality of ramp signals.

It is a block diagram which shows the structural example of the imaging device by this embodiment. It is a block diagram which shows the structural example of an image pick-up element. It is a figure which shows the analog-digital conversion of a pixel signal. It is a figure which shows the difference in the black level of the analog digital conversion of a pixel signal. It is a figure which shows the OB pixel area | region and effective pixel area | region of an image pick-up element. It is a figure which shows the offset of a black level.

  FIG. 1 is a block diagram illustrating a configuration example of an imaging apparatus according to an embodiment of the present invention. The imaging device can be applied to a smartphone, a tablet, an industrial camera, a medical camera, and the like in addition to a digital camera and a video camera. The imaging apparatus includes a photographing lens 100, an imaging element 101, an AGC (automatic gain controller) 102, an image signal processing unit 103, a lens driving unit 104, and a microcomputer 105. The photographing lens 100 includes a zoom lens, a focus lens, a diaphragm, and the like for photographing a subject image, and forms a light image of the subject on the image sensor 101. The image sensor 101 is a CMOS image sensor, for example, and converts light of a subject image formed by the photographing lens 100 into an electric signal. The AGC 102 adjusts the gain of the electrical signal converted by the image sensor 101 based on the luminance of the subject image. The image signal processing unit 103 performs image processing such as gamma correction and white balance correction, resolution conversion processing such as aperture setting, image compression processing and the like on the electric signal whose gain is adjusted by the AGC 102, Convert to a predetermined format such as a still image. The lens driving unit 104 drives actuators such as a zoom lens, a focus lens, and a diaphragm in the photographing lens 100. A microcomputer (hereinafter referred to as a microcomputer) 105 controls the image sensor 101, AGC 102, image signal processing unit 103, and lens driving unit 104.

  Next, a processing method of this imaging apparatus will be described. First, the lens driving unit 104 drives a zoom lens, a diaphragm, and a focus lens in the photographing lens 100 based on a lens driving control signal supplied from the microcomputer 105 to form a subject image on the image sensor 102. Let The image sensor 101 photoelectrically converts a subject image formed via the photographing lens 100 based on a control signal from the microcomputer 105, and generates a digital image signal (hereinafter referred to as digital data) by a built-in analog-digital converter. To do. The microcomputer 105 receives the digital data generated by the image sensor 101 and drives the aperture in the photographing lens 100 by the lens driving unit 104 based on the brightness of the subject image to adjust the amount of incident light. The AGC 102 adjusts the gain of the digital data generated by the image sensor 101 under the control of the microcomputer 105 and outputs the digital data to the image signal processing unit 103. The image signal processing unit 103 performs image processing such as gamma correction and white balance correction, resolution conversion processing such as aperture setting, image compression processing, and the like on the digital data gain-adjusted by the AGC 102, moving images, still images, and the like Is converted into a predetermined format. The predetermined format is AVCHD, JPEG, or the like. The image signal processing unit 103 supplies a moving image or a still image to a display unit such as a panel or a recording medium such as a memory or a hard drive.

  FIG. 2 is a block diagram illustrating a configuration example of the image sensor 101. The image sensor 101 has a slope-type analog-digital converter that performs analog-digital conversion based on a plurality of ramp signals having different inclinations. The pixel unit 200 has a plurality of pixels arranged in a matrix. Each of the plurality of pixels includes a photoelectric conversion element (photodiode) that converts light into electric charge, an amplifier that amplifies a voltage based on the electric charge of the photoelectric conversion element, a reset circuit that resets the electric charge accumulated in the photoelectric conversion element, and the like And is controlled by the vertical scanning circuit 201. The vertical scanning circuit 201 controls the pixel unit 200. Specifically, the vertical scanning circuit 201 resets the pixels in the pixel unit 200 in units of rows, and causes the column amplifier unit 202 to output the signals of the pixels in each column in the pixel unit 200 in units of rows. The column amplifier unit 202 is controlled by the control circuit unit 212, and discretely amplifies the analog pixel signal output from the pixels of each column of the pixel unit 200, such as 1 ×, 2 ×, etc. for each column.

  The REF circuit unit 204 is controlled by the control circuit unit 212 and outputs a reference voltage Vref. The comparison unit 203 of each column compares the analog pixel signal of each column output from the column amplifier unit 202 with the reference voltage Vref output from the REF circuit unit 204. The RAMP circuit unit 206 is controlled by the control circuit unit 212 and outputs a plurality of ramp signals having different inclinations. For example, as shown in FIG. 3, the RAMP circuit unit 206 outputs two types of ramp signal 301 having a high gain and a small slope and ramp signal 300 having a low gain and a large slope. The levels of the ramp signals 300 and 301 increase with time. The slope selection circuit unit 205 of each column is a selection unit, and is controlled by the control circuit unit 212. Based on the comparison result of the comparison unit 203 of each column, a plurality of ramp signals 300 having different slopes output from the RAMP circuit unit 206 are provided. Alternatively, 301 is selected and output. The ramp comparison unit 207 in each column compares the ramp signal selected by the slope selection circuit unit 205 in each column with the pixel signal in each column output from the column amplifier unit 202, and gradually increases the ramp signal and the pixel. A count stop signal is output at the timing when the signal levels match. That is, the ramp comparison unit 207 in each column compares the signal of the OB pixel or effective pixel in each column with the ramp signal 300 or 301 selected by the slope selection circuit unit 205 in each column.

  The counter unit 208 in each column is controlled by the control circuit unit 212. The counter unit 208 of each column resets the counter value to zero at the timing when the RAMP circuit unit 206 starts to generate the ramp signal slope, and from that point until the ramp comparison unit 207 of each column outputs a count stop signal. Count time. That is, the counter unit 208 counts the time until the level of the signal of the OB pixel or effective pixel matches the level of the ramp signal 300 or 301 selected by the slope selection circuit unit 205. For example, the counter unit 208 in each column is a 12-bit counter. The bit shift unit 209 for each column is a multiplication unit, and when the slope selection circuit unit 205 selects the ramp signal 300 having a large slope, the counter value output by the counter unit 208 for each column is digitally quadrupled. (Shift by 2 bits) and store. The above 4 times is a coefficient multiple corresponding to the inclination. In addition, when the slope selection circuit unit 205 selects the ramp signal 301 having a small slope, the bit shift unit 209 of each column stores the counter value output from the counter unit 208 of each column as it is. This counter value is a digital pixel signal. The analog / digital conversion unit includes a comparison unit 203, a slope selection circuit unit 205, a ramp comparison unit 207, a counter unit 208, and a bit shift unit 209. The analog-digital conversion unit converts the analog pixel signal output from the column amplifier unit 202 into a digital pixel signal, and outputs the digital pixel signal to the horizontal transfer unit 210.

  The horizontal transfer unit 210 stores the counter value (digital pixel signal) of each column stored in the bit shift unit 209 of each column for one row, and transfers the digital pixel signal of each column one pixel at a time in the horizontal direction. Forward to. The transfer unit 211 converts the digital pixel signal output from the horizontal transfer unit 210 into a format such as LVDS and outputs the converted signal to the AGC 102 in FIG. The control circuit unit 212 inputs / outputs communication signals to / from the microcomputer 105 in FIG. 1 and controls each block in the image sensor 101.

  FIG. 5 is a diagram illustrating a configuration example of the pixel unit 200. The pixel unit 200 includes an effective pixel area 501 and optical black pixel areas (OB pixel areas) 502 and 503. The OB pixel region 502 is a plurality of rows of vertical OB pixel regions above the pixel unit 200. The OB pixel region 503 is a horizontal OB pixel region of a plurality of columns on the left side of the pixel unit 200. The OB pixel regions 502 and 503 include a plurality of optical black pixels (OB pixels) in which the photoelectric conversion unit is shielded from light, and the OB pixels output a black level signal. The black level is a reference level that serves as a reference for the analog pixel signal. The effective pixel region 501 includes a plurality of effective pixels in which the photoelectric conversion unit is not shielded from light, and the effective pixel outputs a pixel signal corresponding to the photoelectric conversion of the photoelectric conversion unit.

  Next, the operation of the image sensor 101 that performs analog-to-digital conversion using a plurality of ramp signals 300 and 301 having different inclinations will be described with reference to FIGS. 1, 2, and 3. The column amplifier unit 202 includes an analog memory unit for each column that holds an analog pixel signal for each column. The control circuit unit 212 outputs a reset signal to the column amplifier unit 202 and clears the analog pixel signal of the analog memory unit of each column in the column amplifier unit 202. The column amplifier unit 202 outputs a black level signal of the OB pixel in each column of the OB pixel region 502. The lamp comparison unit 207 in each column receives a black level signal of the OB pixel in each column. In that case, the control circuit unit 212 outputs a control signal for selecting the ramp signal 301 having a small slope with a high gain to the slope selection circuit unit 205.

  FIG. 3 is a diagram showing a plurality of ramp signals 300 and 301 having different inclinations. Hereinafter, analog-digital conversion of the image sensor 101 will be described. The horizontal axis represents the 12-bit counter value of the counter unit 208, and the vertical axis represents the voltage value of the analog pixel signal input to the lamp comparison unit 207. The first ramp signal 301 is a ramp signal with a small slope. The second ramp signal 300 is a ramp signal having a large slope. The second ramp signal 300 has a larger slope than the first ramp signal 301.

  For example, the REF circuit unit 204 outputs a reference voltage Vref of 250 [mV]. When the analog pixel signal is in the range of 250 [mV] to 1000 [mV], the slope selection circuit unit 205 selects the ramp signal 300 having a large slope. In that case, the voltage value of the analog pixel signal per 1 [LSB] of the counter value of the counter unit 208 is about 244 [μV].

  When the analog pixel signal is in the range of 0 to 250 [mV], the slope selection circuit unit 205 selects the ramp signal 301 having a small slope. In that case, the voltage value of the analog pixel signal per 1 [LSB] of the counter value of the counter unit 208 is about 61 [μV].

  First, an operation of analog-digital conversion of a black level signal in the OB pixel region 502 will be described. The slope selection circuit unit 205 selects the ramp signal 301 having a small slope because the black level signal is smaller than the reference voltage Vref. The ramp comparison unit 207 outputs a count stop signal to the counter unit 208 at the timing when the level of the black level analog pixel signal in the OB pixel region 502 matches the level of the ramp signal 301 with a small slope. The bit shift unit 209 for each column stores the counter value of the counter unit 208 for each column at that time. For example, as shown in FIG. 3, when the voltage of the analog pixel signal is A [mV], the count value A1 [LSB] of the counter unit 208 when the analog pixel signal matches the ramp signal 301 is the bit shift unit. 209. As described above, the black level signals of the OB pixels for one row in the OB pixel region 502 can be stored as digital values in the bit shift unit 209 of each column.

  Next, an operation of analog-digital conversion of signals in rows of the effective pixel region 501 and the OB pixel region 503 will be described. The effective pixel region 501 is irradiated with incident light of a subject image that has passed through the photographing lens 100 for a predetermined exposure time. Effective pixels in the effective pixel region 501 photoelectrically convert incident light and output pixel signals. The OB pixels in the OB pixel region 503 output a black level signal regardless of the incident light. The pixel unit 200 outputs an analog pixel signal for each column to the column amplifier unit 202 for each row in accordance with a control signal from the vertical scanning circuit 201. The column amplifier unit 202 amplifies the analog pixel signal by applying a discrete analog gain such as 1 ×, 2 ×, or 4 × to the analog pixel signal based on the amount of incident light, and outputs the amplified analog pixel signal. The REF circuit unit 204 outputs a reference voltage Vref of, for example, 250 [mV]. The comparison unit 203 compares the analog pixel signal of the column amplifier unit 202 with the reference voltage Vref. The slope selection circuit unit 207 selects the ramp signal 300 having a large slope when the analog pixel signal exceeds 250 [mV], and the ramp signal 301 having a small slope when the analog pixel signal is 250 [mV] or less. Select.

  Next, with reference to FIG. 3, the analog-digital conversion when the analog pixel signal of the column amplifier unit 202 is 250 [mV] or less will be described. The control circuit unit 212 clears the count value of the counter unit 208 to zero. When the analog pixel signal (effective pixel signal) is equal to or lower than the reference voltage Vref (250 [mV]) (less than the threshold value), the slope selection circuit unit 205 selects the ramp signal 301 having a small slope and outputs the ramp signal 301 as an output. Start. At the same time, the counter unit 208 starts a counting operation. The ramp comparison unit 207 compares the analog pixel signal and the ramp signal 301 and outputs a counter stop signal to the counter unit 208 at a timing when both match. The counter unit 208 transfers the counter value at the coincidence timing to the bit shift unit 209. The bit shift unit 209 stores the counter value. For example, when the analog pixel signal is 100 [mV], the count value of the counter unit 208 is about 1640 [LSB]. Here, 1 [LSB] ≈61 [μV].

  When the analog pixel signal (effective pixel signal) is larger than the reference voltage Vref (250 [mV]), the slope selection circuit unit 205 selects the ramp signal 300 having a large slope and starts outputting the ramp signal 300. . At the same time, the counter unit 208 starts a counting operation. The ramp comparison unit 207 compares the analog pixel signal and the ramp signal 300, and outputs a counter stop signal to the counter unit 208 at a timing when they match. The counter unit 208 transfers the counter value at the coincidence timing to the bit shift unit 209. The bit shift unit 209 stores the counter value.

  As shown in FIG. 3, when the analog pixel signal is B [mV], the count value B1 [LSB] of the counter unit 208 when the analog pixel signal and the ramp signal 300 match is stored in the bit shift unit 209. . When the voltage B [mV] of the analog pixel signal is 500 [mV], the count value B1 of the counter unit 208 is about 2049 [LSB]. Here, 1 [LSB] = 244 [μV].

  Next, when the slope selection circuit unit 205 selects the ramp signal 300 having a large slope, the bit shift unit 209 performs a quadruple operation by shifting the counter value of the counter unit 208 by 2 bits. When the ramp signal 300 having a large slope is selected, the analog-to-digital conversion unit performs analog-to-digital conversion on the analog pixel signal of 250 [mV] to 1000 [mV], so that the counter value of the counter unit 208 is 1024 [LSB] to 4095 [LSB]. In this case, the bit shift unit 209 outputs a count value of 4096 [LSB] to 16380 [LSB] by multiplying the counter value by four.

  When the slope selection circuit unit 205 selects the ramp signal 301 having a small slope, the bit shift unit 209 does not perform 2-bit shift. In this case, the analog pixel signal is 0 to 250 [mV], and the counter value of the counter unit 208 is 0 [LSB] to 4095 [LSB]. Therefore, 0 [mV] to 1000 [mV] have pseudo 14-bit analog-digital conversion gradations from 0 [LSB] to 16380 [LSB].

  Note that the image signal processing unit 103 performs gamma correction with a strong gamma curve for an image with a small pixel signal level, and thus an image with a small pixel signal level requires sufficient gradation. On the other hand, the image signal processing unit 103 performs gamma correction with a weak gamma curve for an image with a large pixel signal level, so an image with a large pixel signal level does not require sufficient gradation.

  The bit shift unit 209 of each column holds the digital data of the black level of each column described above, and subtracts the digital data of the black level of each column from the digital data of the effective pixel of each column, thereby offset components and noise. The digital pixel signal from which the component has been removed is output to the horizontal transfer unit 210. Then, the horizontal transfer unit 210 transfers the digital data of the pixels in each column to the transfer unit 211. The transfer unit 211 sequentially transfers the digital data of the pixels in each column to the AGC unit 102.

  In the present embodiment, the comparison unit 203 and the lamp comparison unit 207 are individually configured. However, since both are comparators, a common configuration may be used. In the present embodiment, the analog-digital conversion process is performed using the ramp signals 301 and 301 having two types of inclinations, but the analog-digital conversion process may be performed using the ramp signals having three or more types of inclinations. . As described above, the image sensor 101 realizes pseudo 14-bit analog-digital conversion by using ramp signals having a plurality of inclinations.

  FIG. 4 is a diagram showing a plurality of ramp signals 300 and 301 having different inclinations. The horizontal axis represents the 12-bit counter value of the counter unit 208, and the vertical axis represents the voltage value of the analog pixel signal input to the lamp comparison unit 207. Hereinafter, a case where a black level signal serving as a reference of an analog pixel signal is converted by a ramp signal 300 having a large slope and a case of conversion by a ramp signal 301 having a small slope will be described.

  When the ramp comparison unit 207 compares the black level analog pixel signal with the ramp signal 301 having a small slope, the counter value of the counter unit 208 is BLKL [LSB]. On the other hand, when the ramp comparison unit 207 compares the black level analog pixel signal with the ramp signal 300 having a large slope, the counter value of the counter unit 208 is BLKH [LSB]. The counter value BLKH [LSB] is smaller than the counter value BLKL [LSB].

  There is a difference between the counter values BLKH [LSB] and BLKL [LSB] by the ramp signals 300 and 301 having different slopes. By subtracting the black level digital data of the OB pixel from the digital data of the effective pixel, the offset component and the noise component are reduced. In this case, the signal of the OB pixel in the OB pixel area 502 and the signal of the effective pixel in the effective pixel area 501 need to be analog-digital converted by a ramp signal having the same slope.

  As shown in FIG. 5, the row direction of the OB pixel region 502 is divided into n rows and m rows. The OB pixel region 502 includes n rows of first OB pixel regions 502a and m rows of second OB pixel regions 502b. The column direction of the OB pixel region 503 is divided into n columns and m columns. The OB pixel region 503 includes an n-column first OB pixel region 502a and an m-column second OB pixel region 503b. For example, the analog-to-digital conversion unit of the image sensor 101 converts the black level signal of the OB pixel in the OB pixel region 502a of n rows from analog to digital using the ramp signal 301 having a small slope. Further, the analog-digital conversion unit of the image sensor 101 converts the black level signal of the OB pixel in the m-row OB pixel region 502b from analog to digital using the ramp signal 300 having a large slope. Specifically, when the OB pixel region 502 has 30 rows, the n rows of OB pixel regions 502a have 15 rows, and the m rows of OB pixel regions 502b have 15 rows. The bit shift unit 209 in each column holds digital data of the OB pixels in the OB pixel regions 502a and 502b in each column, respectively.

  Similarly, the analog-digital conversion unit of the image sensor 101 converts the black level signal of the OB pixel in the n-row OB pixel region 503a from analog to digital using the ramp signal 301 having a small slope. In addition, the analog-digital conversion unit of the image sensor 101 converts the black level signal of the OB pixel in the m rows of OB pixel regions 503b from analog to digital using the ramp signal 300 having a large slope.

  When the slope selection circuit unit 205 selects the ramp signal 301 with a small slope, the analog-digital conversion unit converts the effective pixel signal from analog to digital using the ramp signal 301 with a small slope. In this case, the bit shift unit 209 of each column determines the black level digital data of each column based on the black level digital data of the OB pixel of each column of the n-row OB pixel region 502a. The black level digital data of the OB pixels in the n-row OB pixel region 502 a is data that has been analog-to-digital converted using the ramp signal 301 with a small slope. Then, the bit shift unit 209 of each column subtracts the black level digital data of each determined column from the digital data of the analog pixel signal of the effective pixel of each column of the effective pixel region 501 to obtain the black level. Reduces offset and vertical noise components. Accordingly, the bit shift unit 209 can perform subtraction based on the digital data of the OB pixel and the effective pixel that are analog-digital converted using the ramp signal 301 having a small slope. In this case, the bit shift unit 209 is an arithmetic unit, and the black level (reference level) based on the digital signal of the OB pixel converted from analog to digital using the ramp signal 301 having a small inclination, and the digital signal of the effective pixel, The difference between is output. Note that the image signal processing unit 103 or the bit shift unit 209 may perform processing of the digital data in the effective pixel region 501 based on the digital data in the OB pixel region 503.

  When the slope selection circuit unit 205 selects the ramp signal 300 having a large slope, the analog-to-digital conversion unit converts the effective pixel signal from analog to digital using the ramp signal 300 having a large slope. In this case, the bit shift unit 209 of each column determines the black level digital data of each column based on the black level digital data of the OB pixels of each column of the m rows of OB pixel regions 502b. The black level digital data of the OB pixels in the OB pixel region 502b of m rows is data that has been analog-to-digital converted using the ramp signal 300 having a large slope. Then, the bit shift unit 209 of each column subtracts the black level digital data of each determined column from the digital data of the analog pixel signal of the effective pixel of each column of the effective pixel region 501, thereby obtaining an offset component or Reduce noise components. Accordingly, the bit shift unit 209 can perform subtraction based on the digital data of the OB pixel and the effective pixel that are analog-digital converted using the ramp signal 300 having a large slope. In this case, the bit shift unit 209 is an arithmetic unit, and a black level (reference level) based on a digital signal of an OB pixel converted from analog to digital using a ramp signal 300 having a large slope, and a digital signal of an effective pixel, The difference between is output. Note that the image signal processing unit 103 or the bit shift unit 209 may perform processing of the digital data in the effective pixel region 501 based on the digital data in the OB pixel region 503.

  In the present embodiment, the imaging apparatus divides the OB pixel regions 502 and 503, and converts the black level signals of the OB pixel regions 502 and 503 into analog to digital signals using a plurality of ramp signals 300 and 301 having different inclinations. An example of performing is shown. However, the imaging apparatus may perform analog-digital conversion on the black level signals of the OB pixel regions 502 and 503 using the ramp signals 300 and 301 having different inclinations for each frame. For example, in the first frame, the analog / digital conversion unit converts the signal of the OB pixel in the OB pixel regions 502 and 503 from analog to digital using the ramp signal 301 having a small slope. In the second frame, the analog-digital conversion unit converts the signal of the OB pixel in the OB pixel regions 502 and 503 from analog to digital using the ramp signal 300 having a large slope.

  As described above, the image sensor 101 according to the present embodiment does not perform analog-digital conversion of a black level signal using the ramp signal 301 having a small slope at all times. The imaging device 101 performs analog-digital conversion on the black level signals of the OB pixels in the n-row OB pixel region 502a and the OB pixels in the n-column OB pixel region 503a by using a ramp signal 301 having a small slope. . Also, the image sensor 101 performs analog-to-digital conversion on the black level signals of the OB pixels in the m rows of OB pixel regions 502b and the OB pixels in the m columns of OB pixel regions 503b using a ramp signal 300 having a large slope. I do.

  When the slope selection circuit unit 205 selects the ramp signal 301 with a small slope, the bit shift unit 209 performs subtraction using the digital data of the OB pixel that has been analog-to-digital converted using the ramp signal 301 with the small slope. When the slope selection circuit unit 205 selects the ramp signal 300 having a large slope, the bit shift unit 209 performs subtraction using the digital data of the OB pixel that has been analog-to-digital converted using the ramp signal 300 having the large slope. . As a result, the bit shift unit 209 performs subtraction based on the digital data of the effective pixels and the digital data of the OB pixels that have been converted from analog to digital using the ramp signal having the same inclination, thereby reducing the image quality due to the offset component and the noise component. Can be reduced.

  FIG. 6 is a diagram showing a black level offset component due to temperature or the like during analog-digital conversion. The horizontal axis represents the 12-bit counter value of the counter unit 208, and the vertical axis represents the voltage value of the analog pixel signal input to the lamp comparison unit 207. In the black level digital data, the offset component fluctuates not only due to the fluctuation due to the inclination of the ramp signal but also due to variations in the elements inside the OB pixel and temperature changes after energization.

  The ramp signal 300 is a ramp signal having a large slope. The ramp signal 300ofs is a ramp signal having a large slope in which an offset component is generated. The ramp signal 301 is a ramp signal with a small slope. The ramp signal 301ofs is a ramp signal having a small slope in which an offset component is generated. The counter value BLKH1 is a counter value of the counter unit 208 when the black signal is analog-digital converted using the ramp signal 300. The counter value BLKH2 is a counter value of the counter unit 208 when a black level signal is analog-digital converted using the ramp signal 300ofs. The counter value BLKL1 is a counter value of the counter unit 208 when the black signal is analog-digital converted using the ramp signal 301. The counter value BLKL2 is a counter value of the counter unit 208 when the black level signal is analog-digital converted using the ramp signal 301ofs.

  The offset component OFSH is a difference between the counter values BLKH1 and BLKH2, and is an offset component of the black level counter value when the ramp signal 300ofs including the offset component is used. The offset component OFSL is a difference between the counter values BLKL1 and BLKL2, and is an offset component of the black level counter value when the ramp signal 301ofs including the offset component is used. The offset component OFSH when a ramp signal with a large slope is used is different from the offset component OFSL when a ramp signal with a small slope is used.

  In this embodiment, when the slope selection circuit unit 205 selects the ramp signal 301 having a small slope, the bit shift unit 209 uses the digital data of the OB pixel that has been analog-to-digital converted using the ramp signal 301 having the small slope. Perform subtraction. When the slope selection circuit unit 205 selects the ramp signal 300 having a large slope, the bit shift unit 209 performs subtraction using the digital data of the OB pixel that has been analog-to-digital converted using the ramp signal 300 having the large slope. . The bit shift unit 209 performs subtraction on the basis of the digital data of the effective pixels and the digital data of the OB pixels that have been analog-digital converted using the ramp signal having the same inclination and the same offset component, and the image quality due to the offset component and the noise component is reduced. Deterioration can be reduced.

(Other embodiments)
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in the computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  The above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

200 pixel unit, 201 vertical scanning circuit unit, 202 column amplifier unit, 203 comparison unit, 204 REF circuit unit, 205 slope selection circuit unit, 206 RAMP circuit unit, 207 ramp comparison unit, 208 counter unit, 209 bit shift unit, 210 Horizontal transfer unit, 211 transfer unit, 501 effective pixel area, 502,503 OB pixel area

Claims (8)

An optical black pixel region including a plurality of optical black pixels in which the photoelectric conversion unit is shielded from light;
An effective pixel region including a plurality of effective pixels in which the photoelectric conversion unit is not shielded;
An optical black pixel signal in the optical black pixel region is converted from analog to digital using the first ramp signal, and the optical black is converted using the second ramp signal having a larger slope than the first ramp signal. An analog-to-digital converter that converts an optical black pixel signal in the pixel area from analog to digital, and converts the effective pixel signal from analog to digital using the first ramp signal or the second ramp signal;
When the analog-digital conversion unit converts the effective pixel signal from analog to digital using the first ramp signal, the optical black converted from analog to digital using the first ramp signal When the difference between the reference level based on the digital signal of the pixel and the digital signal of the effective pixel is output, and the analog-digital conversion unit converts the effective pixel signal from analog to digital using the second ramp signal Includes a calculation unit that outputs a difference between a reference level based on the digital signal of the optical black pixel converted from analog to digital using the second ramp signal and the digital signal of the effective pixel. An imaging device that is characterized.   The analog-to-digital conversion unit converts the effective pixel signal from analog to digital using the first ramp signal when the effective pixel signal is less than or equal to a threshold value, and the effective pixel signal is 2. The imaging apparatus according to claim 1, wherein when the threshold value is larger than the threshold value, the signal of the effective pixel is converted from analog to digital using the second ramp signal. The optical black pixel region has a first optical black pixel region and a second optical black pixel region,
The analog-to-digital conversion unit converts the optical black pixel signal in the first optical black pixel region from analog to digital using the first ramp signal, and uses the second ramp signal to 3. The image pickup apparatus according to claim 1, wherein the signal of the optical black pixel in the second optical black pixel region is converted from analog to digital.   The analog-to-digital conversion unit converts the optical black pixel signal in the optical black pixel region from analog to digital using the first ramp signal in the first frame, and converts the signal from the analog to digital in the second frame. 3. The image pickup apparatus according to claim 1, wherein an optical black pixel signal in the optical black pixel region is converted from analog to digital using two ramp signals. The analog-digital converter is
A selector for selecting the first ramp signal or the second ramp signal;
A comparison unit that compares the signal of the optical black pixel or the effective pixel with the first ramp signal or the second ramp signal selected by the selection unit;
A counter that counts a time until a level of the signal of the optical black pixel or the effective pixel matches the level of the first ramp signal or the second ramp signal selected by the selection unit. The imaging device according to any one of claims 1 to 4.   The imaging apparatus according to claim 5, wherein the analog-to-digital conversion unit further includes a multiplication unit that multiplies a counter value of the counter when the selection unit selects the second ramp signal.   The selection unit selects the first ramp signal when the signal of the effective pixel is equal to or smaller than a threshold value, and selects the second ramp signal when the signal of the effective pixel is larger than the threshold value. The imaging apparatus according to claim 5, wherein the imaging apparatus is selected. An imaging device processing method comprising: an optical black pixel region including a plurality of optical black pixels whose photoelectric conversion unit is shielded from light; and an effective pixel region including a plurality of effective pixels whose photoelectric conversion unit is not shielded from light.
An analog-digital conversion unit converts the optical black pixel signal in the optical black pixel region from analog to digital using the first ramp signal, and outputs a second ramp signal having a slope larger than that of the first ramp signal. The optical black pixel signal in the optical black pixel region is converted from analog to digital, and the effective pixel signal is converted from analog to digital using the first ramp signal or the second ramp signal. Steps,
When the signal of the effective pixel is converted from analog to digital using the first ramp signal by the arithmetic unit, the optical black pixel converted from analog to digital using the first ramp signal When a difference between the reference level based on the digital signal of the first pixel and the digital signal of the effective pixel is output and the signal of the effective pixel is converted from analog to digital using the second ramp signal, the second And a step of outputting a difference between a reference level based on the digital signal of the optical black pixel converted from analog to digital by using the ramp signal and a digital signal of the effective pixel. Method.

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